This invention relates to devices for removing condensed liquids from a piping system or equipment while preventing or minimizing the loss of gases or vapors from which they have condensed.
Such devices are widely employed in steam systems for a variety of reasons. These include preventing mechanical damage caused by the shock of water hammer, maintaining the efficiency of heat transfer equipment, reducing the corrosive damage to piping and equipment and maintaining a more efficient system by minimizing the loss of live steam before its heat value can be properly utilized.
Similar devices are also used in compressed air systems to remove condensed water vapor. The reasons for their use are also similar to those for the steam systems, namely, to protect piping and equipment from mechanical shock and corrosion, and to minimize the loss of compressed air before its energy is utilized.
The broad category of prior art devices includes those which cycle between open and closed to remove the intended liquids and those which are designed with a fixed opening to constantly bleed the system. This invention relates to the latter group of fixed opening constant bleed devices. When using a fixed opening, constant bleed device, it is important to engineer the proper size opening for the existing system conditions for each application. If the conditions change, it may become necessary to change the size of the fixed opening.
U S Pat. Nos. 3,715,870 and 3,877,895 describe devices utilizing a plate with a small diameter orifice drilled at its center serving as a restricted flowpath for condensate to be forced through. The plate is inserted in a condensate return line between two flanges and sealed with gaskets. A screening device is incorporated into the gasket at the high pressure inlet side of the plate. These devices provide an efficient condensate bleed when properly sized to line conditions. They have the potential to develop leaks upon deterioration or improper installation of the gasket material. New gaskets are required when changing orifice plates in these assemblies. Flow patterns through them follow those of square-edged orifices. These flow patterns cause edge erosion of the orifice plate and often cause particle build-up at the exit of the orifice plate which can plug the orifice from the back side.
U.S. Pat. No. 4,171,209 describes an orifice plate formed within the body of a fitting which can be connected to standard pipe fittings in a condensate return line. This device incorporates a seated screening device spaced just upstream of the orifice plate formation. In its simplest form, the design of the device eliminates the sealing requirements between the orifice plate and the flanges in the device of the aforementioned patents. In order to prevent the loss of live steam, the inventor states in his preferred embodiments "the apparatuses according to the invention are best designed to have orifices of such size that most but not all of the condensate will be expelled therethrough so that at least some liquid remains within the system at the orifice to prevent loss of steam or other vapor or gas through the orifice." The entire unit must be changed when changes in system conditions warrant a different size orifice plate formation. Flow patterns through these devices also follow those of square-edged orifices. The drawbacks to flow through these devices are the same as those mentioned above.
U.S. Pat. Nos. 4,426,213 and 4,486,208 describe flow constriction devices for drainage of steam condensate, which incorpate the flow characteristics of a tubular nozzle. The bodies of these devices ar designed to receive tubular nozzle inserts in a variety of sizes. This design allows for easier less costly fabrication of the nozzle structure. It also makes possible the interchanging of nozzle structures within the same body when required to meet changes in system condition, e.g., steam pressure. However, due to the design of the apparatus, it is necessary to remove the in-line screening device to gain access to the nozzle structure when replacing it. Also, because the nozzle structures are frictionally mounted within the bore of the body, good seals are not maintained when the nozzle structure is changed. Although the inventor states that the tubular nozzle structure is removably inserted within the bore, it is advisable to replace the whole unit to ensure proper sealing at the point of frictional mounting when changing nozzles within a steam system. In the preferred embodiments of these devices, the cylindrical body piece is milled at 180.degree. intervals to form two seats for engagement by a wrench. Installation and removal can be difficult in areas with limited acces due to the limited wrench engagement surfaces. Furthermore, the cylindrical shape of the body makes it difficult to recognize at a distance as that of a trapping device. Moreover, it also readily accepts pipe insulation and therefore is more likely to be insulated over and hidden from view than a non cylindrical shape.